The nature of the interaction between irreversibly heparinized materials and blood is to be studied. The effect of surface bound heparin on the antithrombin III-thrombin reaction and on platelets will be investigated, by immobilizing heparin onto Sepharose beads using the heparin-poly (vinyl alcohol) coating procedure developed in our laboratory. This coating procedure involves the formation of an acetal bond between the heparin and surface hydroxyl groups. It results in covalently bound heparin which although permanently attached to the polymer surface (elution rate into 3M NaCl less than the assay detection limit of 10 to the minus 4th power microgram/sq.cm.min), still retains its thromboresistance (prolonged PTT and patent AV shunts after two hours). Use of the affinity chromatography procedure of Hatton et al (Thromb. Res., 10, 645, 1977), will enable investigation of the mechanism of heparin accelerated inactivation of thrombin and elucidation of the nature of the heparin-thrombin-antithrombin complex. This can be achieved without the complications of existing systems (heparin desorption, heparin inactivation, specific steric and chemical effects). Platelet adhesion and release induced by surface bound heparin will be determined by measurement of platelet adhesion in an open static test system and by determination of the platelet reactivity factor in a couette flow test system. This information will be used to assess the potential limitations that have often been suggested to the long term use of heparinized materials: enhanced platelet deposition and eventual saturation of the surface with heparin-thrombin-antithrombin complex. It is anticipated that with the intended clarification of these limitations, heparinized materials will find more widespread use in the fabrication of cardio-circulatory assist devices and blood handling equipment.